This invention relates to a high performance vehicle tire having an asymmetrical tread pattern defined by an inboard tread pattern and an outboard tread pattern which provide more balanced wet, dry and snow handling and traction.
With the increase in high performance vehicles the need for high performance tires which give the consumer a feel of maximum control, grip, and handling capability has also increased. In particular, different vehicle tires are known for their handling and traction performance under one or more of the following: dry road conditions; wet road conditions; and bad weather conditions, such as on snow and ice. Certain vehicle tires are designed to maximize their performance under wet conditions, and others are designed to improve their performance in bad weather conditions, not normally encountered in a summer season design. Considerable attention has been given to the problem of designing a tire tread pattern which provides a high level of handling and traction in dry, wet, and snow conditions. These tires are commonly referred to as xe2x80x9call seasonxe2x80x9d tires.
Initially, when the idea of xe2x80x9call seasonxe2x80x9d tires came about, the tires were symmetrical in their tread pattern. That is, the tire tread looked the same on both sides of the mid-circumferential plane. Both sides of the circumferential plane included more design elements, smaller tread blocks, and more lateral groove events. The tires gained snow traction and picked up some minimum wet traction, but gave up a large amount of dry traction. This led to the next advancement where asymmetry was designed into the tire. The tread patterns on either side of the circumferential plane were different. The purpose of the asymmetrical tire was an attempt to increase the overall dry performance primarily on one side of the tire tread and adding some wet performance improvements of the other side while maintaining good snow performance.
One feature of xe2x80x9call seasonsxe2x80x9d tires is the use of lateral design elements in the tire. These consist of major grooves or small inlet cuts which are called sipes. The more of the lateral design elements, the better grip is provided in snow, slush, deep water, and possibly even ice, depending on the temperature at the surface. In an asymmetrical tread pattern tire, the tire is divided into an inboard tread pattern and an outboard tread pattern about the mid-circumferential plane of the tire. The outboard tread pattern typically includes larger tread block, larger design elements, and fewer lateral grooves and sipes to provide dry handling and traction. The inboard tread pattern typically includes smaller tread blocks, smaller design elements and more lateral grooves and sipes to provide better wet and snow handling and traction. However, the typical all-season tire does not have as good a dry road performance as a conventional asymmetric tire, nor as good a wet road performance as a summer tire, but has better snow performance. However, the tire provides somewhat better performance over all seasons for someone who does not want to remove their summer tires and install snow tires during the winter.
In the typical asymmetrical design, the outboard pattern provides dry performance, and the inboard pattern provides wet performance, with the lateral design elements providing snow performance. The inboard pattern is typically designed with more void space and less road contact surface to aid in the bleeding of water away from the tread and improve wet handling performance. This also provides more tread element edges to contact snow. The outboard pattern has larger blocks and fewer lateral elements to provide block rigidity for increased road surface contact but has less void space, which compromises water removal. Thus, the provision of an all season, high performance vehicle tire in which the wet and dry performance is more balanced and not sacrificed to the provision of snow performance is a problem to which much consideration still must be given.
U.S. Pat. No. 5,660,651 discloses an asymmetrical tire design for use in winter driving conditions wherein the inner and outer shoulder treads are asymmetrical. The inner shoulder tread includes sipes having good opening characteristics and the outer shoulder tread is provided with sipes that assure high tread block rigidity.
U.S. Pat. No. 5,421,387 discloses an asymmetrical tire tread wherein the tread rubber volume is equal on the two sides of the mid-circumferential plane of the tread, and the tread grooves decrease in their width toward the inboard side to improve tread wear, snow traction, tire noise, lateral traction, and overall vehicle handling.
U.S. Pat. No. 5,407,005 discloses an asymmetric, nondirectional tire tread in which the net contact area in a first tread half is approximately equivalent to a net contact area in a second tread half, wherein the tread stiffness in the first tread half is preferably higher than the second tread half.
While the prior asymmetrical tread patterns for high performance tires have utilized various combinations of tread elements and design, the prior high performance tires have not satisfactorily found the right combination to provide balanced handling and traction in wet, dry, and snow conditions.
Accordingly, an object of the present invention is to provide an asymmetrical high performance vehicle tire with balanced wet, dry, and snow handling and traction without sacrificing any one seasonal handling capability.
Another object of the present invention is to provide an asymmetrical high performance vehicle tire wherein the water removal capability of the outboard side is improved and the tread block stability of the inboard side is improved without significantly sacrificing the dry and wet performance of the outboard and inboard sides or snow performance.
Another object of the present invention is to provide an asymmetrical high performance vehicle tire wherein the inboard wet tread pattern has increased tread stability for dry performance without sacrificing water removal capacity and wet performance, and the outboard dry pattern has increased water removal capacity without sacrificing tread stability and dry performance.
The above objectives are accomplished according to the present invention by providing a high performance, asymmetric vehicle tire having an asymmetrical tire tread pattern with an inboard tread pattern and an outboard tread pattern defined with respect to a mid-circumferential plane of the tire carcass that provides a more balanced wet, dry, and snow performance. The inboard tread pattern includes a plurality of circumferential inboard tread ribs encircling the carcass with circumferential inboard tread grooves defined between the inboard tread ribs. The outboard tread pattern includes a plurality of circumferential outboard tread ribs encircling the carcass with circumferential outboard tread grooves defined between the outboard tread ribs. The inboard tread ribs and the outboard tread ribs have a rib contact surface and a bottom rib base. The contact surface is the most radially outer portion of the tread that contacts the road surface. An inboard contact surface area is defined by the area of the contact surface of the inboard tread ribs, and an outboard contact surface area is defined by the area of the contact surface of the outboard tread ribs wherein the inboard and outboard contact surface areas are substantially equal. A plurality of lateral grooves are formed in the inboard and outboard tread patterns, and the inboard tread pattern has a higher density of lateral grooves than the outboard tread pattern. Advantageously, the inboard and outboard tread ribs have an average rib width which is generally equal from rib to rib across the asymmetric tread pattern. The average rib width is the circumferential average from rib wall to rib wall at the contact surface. In one aspect of the invention, the inboard and outboard tread grooves include a groove opening having a width between adjacent rib contact surfaces wherein the groove width is generally equal for all the tread grooves. The inboard and outboard grooves include a generally straight groove base extending in the circumferential direction. The groove opening of the inboard tread grooves between rib contact surfaces is generally a serpentine shape.
Advantageously, the width of the groove base of the tread groove increases from the inboard to the outboard side to facilitate water removal and enhance wet handling of the outboard side. The inboard tread grooves have a serpentine shape at the groove opening, wherein the tread grooves generally become progressively more sinusoidal in amplitude across the tread portion from the outboard side to the inboard side. Also advantageously, the groove base of the tread grooves decreases in base width from the outboard side to the inboard side. In a preferred embodiment, the asymmetric tread pattern includes a first outboard groove having a generally straight groove base and groove opening, and the remaining ones of the tread grooves at the groove opening having an increasingly sinusoidal amplitude across the tread pattern towards the inboard side. The groove openings have a width which is generally equal for each of the groove openings across the tread pattern. The sinusoidal tread grooves are created by rib walls of adjacent tread ribs which taper outwardly and upwardly radially from the groove bases to the rib contact surfaces so that the rib bases have an area greater than the rib contact surfaces providing increased inboard tread rib strength and stability to enhance dry handling performance of the inboard tread portion. The taper of the rib walls increases from the outboard side toward the inboard side of the tire. The tapering rib walls have a taper angle which varies and shifts laterally from side-to-side in the circumferential direction of each tread groove. The taper angle of the outboard tread grooves is less than the inboard grooves to increase water removal from the outboard tread pattern to improve wet performance.